We are currently studying the causes of bile secretory failure in infants and children with cholestatic liver disease. For the current year the studies in progress are: (1) Using balance techniques, quantitatively estimate the excretion of individual bile acids and bile acid sulfates in urine and feces. (2) Prepare and evaluate various stable isotopes of chenodeoxycholic and cholic acid, for the study of bile acid kinetics. (3) Continue to evaluate the diagnostic and therapeutic usefulness of serum bile acid patterns and their changes following cholestyramine administration in distinguishing between neonates with patent bile ducts and those with extrahepatic biliary atresia.